What happens when lithium-ion batteries overheat and explode?

In a paper published yesterday in Nature, researchers at University College London (UCL) documented their process for simultaneously imaging both the inside and outside of lithium ion batteries as they overheat.

The team – led by UCL PhD student Donal Finegan and Dr Paul Shearing, both from the Department of Chemical Engineering – used x-ray images along with thermal images of the batteries in order to improve their understanding of what happens as the battery overheats and enters the process of “thermal runaway.” In this particular set of experiments, these researchers heated two fully-charges commercial lithium-ion batteries to more than 250 degrees C using a heat gun. The x-ray images were captured at a rate of 1,250 frames per second.

These experiments purportedly represent the first time that researchers have used x-rays and thermal images to simultaneously examine the interior and exterior of lithium-ion batteries in the process of overheating. During this project, the UCL team observed that gas pockets were produced as the battery began to overheat. In turn, these gas pockets deformed the batteries and then led to internal short circuits as conductive portions of the battery’s interior came into contact. The scientists hope that this information can be used to improve the battery’s design to make them safer to transport and use.

Hundreds of millions of lithium-ion batteries that are manufactured and transported each year for use in powering mobile phones, laptops, cars and planes. While battery failures are rare, the U.S. Federal Aviation Administration (FAA) have released findings regarding the safety risks associated with transporting these batteries in bulk. These findings sparked high levels of interest in the media just before Christmas and have led airlines including United, Delta, and American to restrict or ban bulk shipments of lithium-ion batteries in their cargo planes.

Photo Credit: UCL